Buyer Beware – hs-cTn Assays Are Not the Same

Written by Clay Smith

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When comparing three commercially available high sensitivity cardiac troponin (hs-cTn) assays, results differed dramatically from one assay to another. The difference was great enough to impact patient care decisions, such as admission, discharge, or further testing.

Why does this matter?
When it comes to hs-cTn, the FDA recommends using the assay-specific cutoffs, such as the lowest level of detection (LOD) or ≥99th percentile. There are three FDA-approved assays made by Roche, Abbott, and Siemens. One would hope that even though the assays may differ in LOD, that the three tests would still give the same answer if run on the same patient’s sample. Is that the case?

Caveat emptor
This was a secondary analysis of patients originally recruited for ROMICAT I and II who had blood samples drawn at various times. They took 1,027 samples from 624 patients and ran them on three different commercially available hs-Tn instruments: Roche Elecsys 2010; Abbott ARCHITECT i2000SR; Siemens HsVista. All patients were intermediate risk for ACS who had been referred for non-invasive testing. Authors identified four key findings. 1) Agreement among the three assays – comparing <LOD, LOD to 99th percentile, and ≥99th percentile – occurred just 37.4% of the time. 2) When the data were analyzed on a per-patient basis, using the 0 and 2 hour hs-cTn from the ROMICAT II cohort, there was agreement among the assays 74.7% of the time on which patients ruled out for MI, which patients needed observation just 15.7% of the time, and which patients ruled in for MI a paltry 38.5% of the time. 3) Agreement among assays was better when the general 99th percentile was used, but when the sex-specific assay cutoffs were used, agreement dropped precipitously. 4) Finally, obstructive CAD was found in 20% of patients with hs-cTn levels <LOD. These are all disturbing findings. Two assays tested troponin-I (Abbott and Siemens) and one troponin-T (Roche), but the authors contended that, “these differences are assumed to be incorporated and reflected by the recommended thresholds,” and did not think the differences were due to troponin isotype. The authors noted the Siemens assay was in a pre-commercial stage and may have been different than the final commercial version. There were also numerous conflicts of interest declared. However, many authors received funding from more than one of the manufacturers, making it less likely they would have a bias to one over another. In short, these differences, up to two-fold between hs-cTn assays, were great enough to impact patient management decisions, such as non-invasive testing, admission, or early discharge. Be aware that different facilities use different assays, and what may be positive at one is not at another. This could lead to differences in management simply based on which assay is used. Ultimately, we need a larger, diverse sample bank of normal healthy patients from which to compare all assays when setting cutoffs.

Source
Discordance of High-Sensitivity Troponin Assays in Patients With Suspected Acute Coronary Syndromes. J Am Coll Cardiol. 2021 Mar 30;77(12):1487-1499. doi: 10.1016/j.jacc.2021.01.046.

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